This invention relates to a method for operating a coal dust furnace (e.g. a cyclone furnace, SU or turbulent smelting furnace, coal dust furnace with dry ash removal, etc.), in which a mixture of combustion air and combustion coal dust having a specified range of grain sizes is blown into the furnace, the range of grain sizes having an upper limiting grain size, and where means are introduced into the furnace for cooling the flame, this means taking part in the combustion, in order to reduce the combustion temperature. As is well known, the cooling of the flame serves to reduce the formation of nitrous oxides.
Amongst known measures, cold combustion air is introduced as a means for reducing the formation of nitrous oxides. However, the reduction effect achieved is not satisfactory and, in addition, these measures for directly cooling the flame have a disadvantageous effect on the stability of the flame. Moreover, there can be a deterioration in the burning off of carbon, that is, the flue dust and ash or slag contains more carbon. The reduction of the formation of nitrous oxides by directly cooling the flame is therefore not very common in practice in coal dust furnaces. Furthermore, basic investigations have shown that nitrous oxide formation from fuel nitrogen still occurs even when the temperature of the flame has been considerably decreased by introducing cold combustion air. In practice, therefore, other measures for reducing the formation of nitrous oxides have been used, namely near stoichiometric combustion, multi-stage combustion and recirculation of waste gas and in particular the use of fuels which are low in nitrogen.
In contrast to this, the present invention sets out to provide a method for operating a coal dust furnace such that an effective reduction in the formation of nitrous oxides is achieved, also in relation to the formation of nitrous oxides from the fuel nitrogen.